Wigner3j symbol

Wigner3j( J123, M123) calculates the Wigner 3j-symbol according to Racah formula.
The Wigner 3j symbol is useful for multiplication of Spherical Harmonics (and their generalizations) and for addition of angular momentum.
The are related to the Clebsch-Gordan coefficients by:
Wigner3j( J123, M123 ) = <J1,J2,M1,M2| J1,J2,J3,-M3> * (-1)^(J1-J2-M3) * (2*J3+1)^(-1/2).
This function is not limited to the factorial limitation (170), so it can be useful for any value of J.

Instead of returning zero when the triangle rule abs(j1-j2)<=j3<=(j1+j2) or the projection addition rule m1+m2=m3, this program instead returns an error message. In my opinion this is not how a Three-J script should work, since many programers will want to apply a Three-J even in cases where it is trivially zero. The script should be modified to return zero when the Three-J is trivially equal to zero.